“Visual field” means the spatial array of visual sensations available for observation by a subject. “Field of view” means the physical objects and light sources in the external world that impinge the subject's retina. In other words, field of view is everything that (at a given time) causes light to fall onto the retina. The field of view is processed by the visual system, which computes the visual field as the output. In optometry and ophthalmology a visual field test is used to study a subject's visual field.
There are many pathological causes of visual deterioration. The pathology can involve the eye itself, the optic nerve, or the neuro-visual pathways in the brain. Knowledge of the visual field together with other ophthalmologic characteristics can help to localize the probable site of the pathology. Certain diseases can cause local scotoma or more extensive losses of vision. Visual field testing may be applied to determine whether the visual field of a subject is affected by disease. In addition to various disorders of the eye a visual field test can be used to help diagnose neurological disorders such as pituitary adenomas (very common brain tumors), meningiomas, cavernous angioma, anterior ischemic optic neuropathy, aneurysm and strokes.
Visual field testing may be performed by a technician directly, by a technician with the assistance of a machine, or by an automated machine. Names applied to visual field testing include perimetry, tangent screen exam, automated perimetry exam, Goldmann visual field exam, or Humphrey field exam. “Perimetry” is the systematic measurement of differential light sensitivity in the visual field by the detection of the presence of test targets on a background.
Techniques for visual field testing include:                Confrontation visual field exam—An examiner asks the subject to cover one eye and stare at the examiner. The examiner then moves a hand out of the subject's visual field and then brings it back in. The subject signals the examiner when the hand comes back into view.        Tangent screen exam or Goldmann field exam—The subject is asked to sit in front of a screen with a target on the center. The eye that is not being tested is covered. While the subject stares at the target the examiner moves an object toward the subject's visual field. The subject signals the examiner when the object comes into view. This exam allows the subject's visual field to be mapped.        Automated perimetry exam—The subject sits in front of a concave dome with a target in the center. The eye that is not being tested is covered. A button is given to the subject to be used during the exam. The subject is set in front of the dome and asked to focus on the target. A computer then causes lights to shine on the inside of the dome and the subject clicks the button whenever a light is seen. The computer then automatically maps and calculates the subject's visual field.Human visual perception is dynamic. It responds well to moving targets. Current instruments for visual field testing typically utilize either a static or a kinetic (moving) dot in detecting scotomas (blind spots).        
Current instruments for visual field testing generally have a degree of subjectivity. They require that the subject's eye remain fixed on a non-moving feature, normally in the center of a screen, while many targets, usually of equal size, are presented in different areas of the subject's visual field. The subject is required to press a button or otherwise deliberately indicate when a target is detected. The required fixation tends to quickly induce fatigue. In addition, the tests tend to be lengthy which further increases fatigue. The requirement for fixation, which is difficult to maintain coupled with the induced fatigue together with the need for a subjective response tends to limit the accuracy. Generally the display of current instruments is curved so that a target is presented at approximately the same distance from the eye being checked anywhere on the screen.
Technology relating to eye testing is disclosed in the following United States patents:                U.S. Pat. No. 3,718,386        U.S. Pat. No. 3,883,235        U.S. Pat. No. 4,059,348        U.S. Pat. No. 4,392,725        U.S. Pat. No. 5,220,361        U.S. Pat. No. 5,319,398        U.S. Pat. No. 5,459,536        U.S. Pat. No. 5,491,757        U.S. Pat. No. 5,880,812        U.S. Pat. No. 5,953,102        U.S. Pat. No. 6,494,578        U.S. Pat. No. 6,527,391        U.S. Pat. No. 6,736,511        U.S. Pat. No. 6,783,240        
There are a variety of devices which work on a variety of principles and purport to be able to track the direction of vision of an eye. Recent studies on active illumination-based approaches show that a multiple infrared (IR) source-synchronized, or active IR, camera is able to robustly locate human pupils under different illumination conditions, even for people wearing eye glasses, from considerable distances.